1. Field of the Invention
The present invention relates to an improvement of an image forming apparatus such as a scanner printer, etc.
2. Description of the Prior Art
Conventionally, this type of image forming apparatus has a construction such as shown in FIGS. 1 and 2.
FIG. 1 shows a scanner printer. A document table (transparent glass) 2 is provided on the upper surface of a housing 1 for placing documents. On one side of document table 2, there is a positioning scale 3 which serves for positioning of a document A. Above document table 2 there is a document cover 4 whose rear edge is pivotally mounted by a shaft (not shown) permitting it to open or to close on document table 2.
An inlet 6 and an outlet 7 by which paper (image-receiving material) P may enter and leave a serial printer unit 5 that is described below are provided at the upper surface of the rear side of housing 1. A control panel 8 is provided at the upper surface of the front side of housing 1.
In housing 1, a scanner unit 9 for reading the image of a document A placed on document table 2 is provided along with serial printer unit 5 which forms images on paper P on the basis of information read by scanner unit 9. Scanner unit 9 is located below document table 2 and serial printer unit 5 is located to the rear side of scanner unit 9.
Scanner unit 9 includes a sensor unit 10 which picks up the image of document A placed on document table 2 and a drive mechanism (not shown) by which sensor unit 10 is moved reciprocally in a front to rear direction (XI direction) and to the left and right direction (Yl direction).
The structure of sensor unit 10 is such that a document surface is illuminated by a spot light and the light reflected from it is led to and focussed at an image sensor, constituted by a charge coupled device (CCD), via a mirror and a lens.
Serial printer unit 5 has a construction as shown in FIG. 2. A cylindrical platen 11 supports and transports paper P. Platen 11 is driven at successive set pitches by a pulse motor 13 acting via a reduction gear train 12. In front of and facing platen 11, a thermal print head 14 as a recording head is provided. Thermal print head 14 can be moved parallel to the axis of platen 11 by a head moving means.
A shaft 15 is provided parallel to platen 11 and a carriage 16 is slidably mounted on shaft 15. Carriage 16 is connected to a timing belt 17 which is passed around between pulleys 18 and 18 that are provided near both ends of shaft 15. One of pulleys 18 can be driven by a pulse motor 20 acting via a reduction gear train 19. Carriage 16 carrying thermal print head 14 is moved reciprocally along a line parallel to the axis of platen 11 by the rotation of pulse motor 20.
Thermal print head 14 has heating elements (not shown) which are arrayed in a direction that intersects the line of the axis of platen 11 at right angles, i.e., parallel to the direction of rotation of platen 11.
A flexible cable 21 has one end fixed by a holder (not shown) to carriage 16, and a connector member 22 provided at its other end is connected to a connection element (not shown) that is located in the approximate center of the path along which carriage 16 moves. The heating elements of thermal print head 14 are connected to a head drive circuit (not shown) via the wiring pattern of the flexible cable 21.
A paper guide 23 and a paper hold-down roller (not shown) are mounted to the outer periphery portion of platen 11.
If paper P is heat-sensitive paper, images are formed by bringing the thermal print head 14 directly against it. If it is plain paper, etc., a ribbon cassette 24 is mounted at the rear side of housing 1 as shown in FIG. 1 and images are produced with a thermal transfer ink ribbon 25 interposed between paper P and thermal print head 14, as shown in FIG. 2.
However, since the arrangement in the above-described conventional apparatus provides serial printer unit 5 in housing 1, the print speed is relatively lower than that of a line printer unit. Generally, a line printer unit can print a larger number of dots in a predetermined time period than can a serial printer unit. Therefore, a serial printer unit has been recently developed to perform high speed printing by controlling the printing operation to skip blank portions. However, the above-mentioned improved serial printer unit is no match for a line printer unit.
Further, since the arrangement in the abovedescribed conventional apparatus is one in which thermal print head 14 is located in front of platen 11, ribbon cassette 24 must be mounted at the rear side of the housing 1 as shown in FIG. 1. Alternatively, it must be set in a portion of the housing 1 interior that is in front of thermal print head 14, i.e., it must be set together with a winding mechanism on carriage 16 for moving thermal head 14.
Both these arrangements hinder production of a more compact apparatus, since in the former arrangement in which ribbon cassette is mounted at the rear side of housing 1, the dimensions going towards the rear are larger when a ribbon cassette is in place, while in the latter arrangement in which the ribbon cassette is mounted on carriage 16, the depth dimension of housing 1 itself becomes large.
Furthermore, since the setting of the paper P in the above-described conventional apparatus depends on personal experience, inexperienced people sometimes cause the paper to misfeed or skew.